The invention relates to sprue cups used in metal casting processes, and, more particularly, to such sprue cups that are disposable.
Sprue cups used in metal casting processes can be either permanent, i.e., made of metal, or disposable. Permanent or metal sprue cups last indefinitely, but they have several disadvantages. Because they are permanent, they must be retrieved for reuse after each casting process is completed. Because they are made of metal, they absorb a great deal of heat, and therefore the molten metal poured into the sprue cup must be heated to a higher temperature than would be necessary if the sprue cup were made of a non-metal. Furthermore, metal sprue cups must be kept coated with a refractory coating, and this necessitates frequent recoating of the sprue cup. Finally, permanent sprue cups require general maintenance so that they are in a suitable condition for use.
Disposable sprue cups, on the other hand, do not have these disadvantages. Disposable sprue cups are typically made of a ceramic material or a fibrous refractory material. Disposable sprue cups generally last through only one casting process and therefore need not be retrieved, recoated, or maintained for reuse. Additionally, ceramic and fibrous refractory materials absorb relatively little heat, so that the molten metal need not be heated higher than is necessary to pour the casting.
The major disadvantage of known disposable sprue cups is that they break down into the process sand of the casting process. As a result, the process sand must be screened out in order to remove either refractory fibers or pieces of ceramic material. Otherwise, the process sand would become contaminated and would not produce satisfactory castings.
Attention is directed to the following U.S. patents:
Zoda U.S. Pat. No. 1,657,952, issued Jan. 31, 1928; PA1 Gans, Jr. U.S. Pat. No. 2,784,467, issued Mar. 12, 1957; PA1 Hoefer U.S. Pat. No. 2,835,007, issued May 20, 1958; PA1 Snelling U.S. Pat. No. 3,526,266, issued Sept. 1, 1970; PA1 Larsen et al. U.S. Pat. No. 3,841,846, issued Oct. 15, 1974; and PA1 Yamasaki U.S. Pat. No. 4,154,285, issued May 15, 1979.